Energy Efficiency Problem

[mechie101]

A customer has a central chilled water and steam plant that runs continuously year-round. Domestic hot water is created from the steam plant. The estimated hot water needed annually is 23,267 MMBTUs. The proposed measure is to install 4 water source heat pumps to heat the domestic hot water. The proposed equipment will create an additional 145 tons of chilled water while using the heat rejection loop to heat the hot water.

Baseline System

Chiller plant - 145 tons to be replaced annually. 0.75 kW/ton

Boiler Plant - 23.267 MMbtus to be replaced. 76% plant efficiency

Proposed System

4 WSHP - 145 tons total, 1.848 kW/Ton, condenser 2.656 mmbtu/hour

Will there be any energy savings for this customer, and if so, how much?

 

[EnergyProfessional]

unless you screw up the design, energy will be saved. How much? Energy Simulation.

 

[mechie101]

Do you have any further insight on to the savings amount ( besides an energy sim) would be very helpful! something brief does not need to be exact

 

[EnergyProfessional]

Unfortunately this is not possible with the information given. And how do you imagine the energy saving numbers should appear without a simulation? Energy consumption in this case will depend on the climate, specific type of equipment (inc. pumps etc.) and their efficiencies. Efficiencies also change with operating conditions (COP depends on temperatures etc.). Climate, amount of hot water used, ground temperature (assumed cold water temp).... a lot to go in and simulate over 8760 hours.

 

[mechie101]

Thank you for the information. Lets say we make the following assumptions:COP of 2.5. Temp in = 50. Temp out = 150. Is there any way I can calculate the savings based on this information and any other assumptions that need to be made?

 

[EnergyProfessional]

No. You don't know what the load of the building does every hour. And COP is not 2.5 all the time, that changes with fluid temperatures. Like in winter the cold water is colder, so COP can be higher. But you may or may not have a cooling load, so you may not have heat recovery.

With the very same system and building you would have more saving opportunity in Florida because you have more hours with cooling load. and do you have cooling 24/7? Cooling an office, or a 24/7 server room? What about water load times? If you are in Alaska, you may have no cooling load, so no heat recovery at all, or only a few hours every year.

you only save energy whne you use hot water, and cool at the same time. If you add a storage tank, this gets a bit better, but also more complex.

 

[nuuvox000]

Yes, there will be savings. As far as how much you'll need to make a lot of assumptions.

Basically, how much money does the baseline water heater system take to heat the water every year? You'll have to make assumptions on use and load here and use the baseline systems kW/ton (assuming electric?, if heat pump then you'll need to figure out which COP you'll use).

Then do the same thing with the heat pump water heaters. Then do the same thing for the chillers (how many BTU's do they not have to transfer because of the water heaters? convert kW/ton to $$$). Then it's just simple addition and subtraction.

If you want a real number then you'll need to do energy modeling like energyprofessional mentioned; this is usually pretty expensive to sub out. I don't know all of the details of your project but maybe they'll be okay knowing they'll save money (what is the baseline?) If it's from air-source heat pump water heaters to water-source heat pump water heaters then it's likely worth the money. You'll have to do a back of the envelope calc to make sure.

 

[mechie101]

Understood, thank you.I really appreciate everybody's help. The baseline heating system for the DHW is a gas fired steam boiler. The electric rate is $0.15 per kWh and the gas rate is $0.65 per therm. As for load use, you are correct I would need some sort of trending data here

 

[mechie101]

I need to get some numbers associated with this problem. Here's what I came up with (I understand there are a lot of assumptions that would need to be verified)